Effects of process-generated hydrogen on RPV walls

5. Hydrogen production in PWR

of them, varying between 50 to 150 mol H per year with one higher value of 650 mol H per year. A note to make with these calculations is that the experimental values of the passive currents is measured for SS304 material, which is slightly different in chemical composition to the SS308L/SS309L material used as stainless steel lining for the RPV of Doel 3 and Tihange 2. However, these values can be used as a good approximation for the corrosion rate of the real material. 5.4 Radiolysis in the primary water The third source of hydrogen, that is needed to be considered is due to the radiolytic dissociation of water molecules in the primary water. Several researchers have tried to make a model for the radiolysis in the primary water of a light water reactor. The first model can be traced back to Burns and Moore [64], trying to model the corrosion of zircaloy claddings in reactor. Their model considered 12 different species and 28 chemical reactions. This model has later been improved by lots of work from Elliot and Christensen [65, 66]. Over the past years also Macdonald and Engelhardt worked intensively on the modeling of radiolysis in the primary water of BWR’s and PWR’s. [48] They provided the model, used as a basis for the calculations concerning radiolysis in this report. The number of species incorporated in the model has increased to 22 with a total of 60 chemical reactions, as this improved reliability and accuracy of the model. The complete code used for the simulations and calculations is attached in Appendix A. 5.4.1 Radiolysis model The chemistry of the primary system is determined by the concentration of boron, added in the pressurizer as B(OH) 3 , Lithium, as LiOH, O 2 , H 2 O 2 , H 2 . Furthermore, the temperature and different types of radiation in the reactor are considered as parameters in the model. The complete model can be found in attachment. The added concentrations of B(OH) 3 , Li(OH), O 2 , H 2 O 2 and H 2 serve as the starting point for the model. Using this values a time dependent concentration change for each considered specie is calculated. The complete set of species considered is:

1. e – 2. H

9. H 2 O 2 10. HO – 2 11. HO 2 12. O – 13. O 14. O 2– 2 15. Li + 16. LiOH

17. LiB(OH) 4 18. B(OH) 3 19. B(OH) – 4 20. B 2 (OH) – 7 21. B 3 (OH) – 10 22. B 4 (OH) 2– 14

3. OH 4. H + 5. OH – 6. O 2 7. O – 2 8. H 2

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